1. In-house MAPREC test of all OPV lots submitted to CBER for release was performed. 2. Control virus samples for Type 3 molecular assay, MAPREC, were prepared and their validation initiated. 3. Study of the effect of addition of inert incipient (lactose) to the MAPREC DNA primers was performed. Bulk amount of primers for OPV 3 MAPREC was prepared in collaboration with the NIBSC, UK. 4. The WHO Collaborative Study on MAPREC with Type 3 OPV was continued. Phase C of the Study was designed, necessary manuals, documentation and materials prepared and shipped to fifteen participants. Progress of the Study was monitored, and trouble shooting and other help provided when requested by the participants. The data collected, analyzed, and report distributed to all the participants and the WHO organizers. A final meeting of the participants is being prepared. 5. Study of genetic stability of Types 1 and 3 OPV in the CNS of monkeys was performed. Mutations occurring upon replication attenuated polioviruses in the CNS were identified. Succession of different types of mutations in the course 1 virus replication in the CNS was studied. 6. Study of properties and genetic composition of Type 3 constructs with mutations introduced by site directed mutagenesis was performed. 7. Foreign scientists were trained in using MAPREC.8. Collaboration with OPV manufacturers on introduction of MAPREC for evaluation of acceptability of OPV was continued. Efforts were concentrated on Type 2 OPV that failed the monkey neurovirulence test and which was produced in a new cell substrate. The project will be continued. Three papers were published.